JP2012137799A - Laser beam generator and optical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized laser beam generator capable of stably oscillating continuous light of a wavelength region of about 200 nm or less at high conversion efficiency.SOLUTION: The light of a wavelength λoutput from a first laser beam generator 10 and the light of a wavelength λoutput from a second laser beam generator 11 are supplied into a first resonator 13 and a second resonator 14, respectively, and the light of a wavelength λis generated by sum frequency blending of the two incident lights in a nonlinear optical element 15 included in both of the first resonator 13 and the second resonator 14. In this case, the lights of the wavelengths λ, λ, λare made incident on and emitted from the nonlinear optical element 15 in a mutually and spatially separated state, and they have mutually different light paths. The lights of the wavelengths λ, λare set so that their optical axes do not completely match with each other, and if the angle of incidence or the angle of emission of one of these lights is the Brewster angle, reflection loss is further reduced.

Description

  The present invention relates to a laser beam generator serving as a light source in an ultraviolet microscope and optical devices such as inspection devices for various electronic materials and electronic components, and more particularly, a laser beam generator that generates ultraviolet light having a short wavelength of about 200 nm or less. About.

  Since laser light is light having a uniform wavelength and phase, the laser light is excellent in monochromaticity and directivity and has a feature of interference. Moreover, it can be converged very finely and can irradiate a minute area. Furthermore, laser light generally has a higher frequency than radio waves and a large capacity for information accommodation. Due to these characteristics, laser light is applied in various fields such as information communication processing field, microfabrication field, measurement field and medical field.

  The performance of a device using such laser light as a light source is generally determined by the wavelength of the laser light and its output stability. For this reason, lasers having a short wavelength have been developed in the past, but continuous light that can sufficiently satisfy the conditions in practical use has not yet been obtained for laser light having a wavelength of about 180 nm to 204 nm. Only light was used. For this reason, it is difficult to use laser light having a wavelength of about 180 nm to 204 nm in a technical field such as mastering of an optical disc that requires continuous light or quasi-continuous light such as mode-locked light. In the fine structure inspection apparatus, when pulsed light is used, there is a possibility that the optical system and the object to be exposed or inspected may be damaged by the high peak power.

For example, continuous light having a wavelength of about 204 nm or more is incident on a BBO (beta-barium borate; β-BaB ₂ O ₄ ) crystal cut out at a phase matching angle, for example. Harmonic Generation (SHG) can be generated relatively easily. However, generation of continuous light of about 204 nm or less by this method has not been achieved so far.

  On the other hand, there has been reported a method of continuously oscillating ultraviolet rays having a shorter wavelength (about 200 nm or less) using the sum frequency of near infrared light and ultraviolet light (about 200 to 400 nm). For example, Watanabe et al. Have proposed a device that generates 194 nm light, which is the third wavelength, by making both an argon ion laser SHG and titanium sapphire laser light enter a nonlinear optical crystal (see Non-Patent Document 1). ). Patent Document 1 proposes an apparatus that generates light having a third wavelength of 193 nm by sum frequency mixing of the fourth harmonic of a YAG laser and titanium sapphire laser light. These techniques improve the conversion efficiency by resonating the above two input waves together, and have a structure in which a part of the optical path in the resonator is shared by the two input waves.

Japanese Patent Laid-Open No. 10-341054

M.Watanabe et.al., Optics Communications, vol.97, pp.225-227 (1993)

  However, it is extremely difficult to coat the optical components arranged on the shared optical path so as to satisfy the low-loss condition at the same time for each wavelength of the input wave. Therefore, such a structure has a problem that the resonator finesse is lowered and it is difficult to efficiently perform wavelength conversion. For example, in the experimental result by Watanabe et al., The multiplication factor of the ultraviolet light by the resonator is suppressed to about 5 times.

  In the latter example, the generated ultraviolet light having the third wavelength is separated from the two incident lights by the wavelength separation mirror. This mirror is also required to be highly reflective with respect to two input waves and at the same time have high transmission with respect to the output wave. As in the previous case, it is difficult to realize such a mirror, and efficient wavelength conversion is achieved. It was difficult to do. In this case, if the output light intensity is increased, two high-intensity ultraviolet rays overlap with each other on the coaxial optical path, which may cause destruction of the apparatus. In order to ensure the ultraviolet durability of the optical system at such a high output, the coating material is limited by this requirement, which may lead to a decrease in conversion efficiency.

  In addition, the titanium sapphire lasers used in these technologies have a very wide tuning frequency range, so they can be locked to a reference resonator or referenced to gas absorption lines to stabilize their absolute wavelength over time. It has been necessary to make the device more complicated.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a laser beam generator capable of stably oscillating continuous light in a wavelength region of about 200 nm or less with high conversion efficiency, and capable of being downsized. And providing an optical apparatus using the same.

  A laser light generator according to the present invention includes a first laser generator that outputs laser light having a first wavelength, a first resonator that resonates laser light having a first wavelength, and laser light having a second wavelength. Are arranged so as to be included in the first resonator and the second resonator, and are arranged at both ends of the second laser generator and the second resonator for resonating the laser light of the second wavelength. A first wavelength laser that includes a nonlinear optical element having an incident surface on which a laser beam having a first wavelength and a laser beam having a second wavelength are incident and an exit surface that emits the laser beam, and passes through the inside of the nonlinear optical element. Non-linear optical element of laser light of first wavelength and laser light of second wavelength in laser light generator for generating laser light of third wavelength by sum frequency mixing of light and laser light of second wavelength The incident angle with respect to The non-linear optical element is a type 1 phase matching and has a beam center axis spatially separated from each other in the first wavelength laser beam and the second wavelength laser beam. The laser light having the first wavelength, the laser light having the second wavelength, and the laser light having the third wavelength are incident on the nonlinear optical element from the incident surface with the beam center axes spatially separated from each other. The first wavelength laser beam and the second wavelength laser beam partially overlap each other within the nonlinear optical element, but the optical axes are not shared. First, the difference in incident angle (separation angle Δθ) between the laser light of the first wavelength and the laser light of the second wavelength with respect to the nonlinear optical element is the difference between the laser light of the first wavelength and the second wavelength of the nonlinear optical element. Laser light input It is larger than twice the beam divergence angle of light (phi).

  In the laser beam generator according to the present invention, the laser beam having the first wavelength and the laser beam having the second wavelength are incident on the nonlinear optical element at different incident angles, so that incident conditions corresponding to the respective wavelengths are determined. The first and second resonator losses are reduced. When the laser light of the first wavelength and the laser light of the second wavelength have the same refraction angle with respect to the nonlinear optical element, the optical axes are parallel to each other and the refraction angles are different. The optical axes do not coincide with each other, and the beams are not shared except for the partial superposition of the beams for the sum frequency mixing.

  The optical apparatus according to the present invention includes the laser beam generator according to the present invention, and is applied to a microscope, various analysis / inspection apparatuses, a disk mastering apparatus, and the like.

  According to the laser beam generator of the present invention, the laser beam having the first wavelength and the laser beam having the second wavelength are spatially separated from each other, satisfy a predetermined condition, and are changed from the incident surface to the nonlinear optical element. The incident laser beam having the first wavelength, the second wavelength laser beam, and the third wavelength laser beam are emitted from the emission surface in a state of being spatially separated from each other, and each has a different optical path. In addition, inside the nonlinear optical element, the laser light of the first wavelength and the laser light of the second wavelength partially overlap, but the optical axis is not shared, so that the optical loss is greatly reduced. In addition, the wavelength conversion efficiency in the sum frequency mixing or the output of the laser light having the third wavelength which is the sum frequency can be improved.

  Since the three laser beams have different optical paths, the first resonator and the second resonator are configured not to share the internal optical path. Loss does not occur, and the resonator loss as a whole is prevented from increasing, and can be operated more stably for a long time. At the same time, the optical element in the resonator does not require a coating corresponding to a plurality of wavelengths, so that an optical loss due to such a coating can be omitted and the apparatus can be simply configured and the cost can be reduced.

  Further, since the laser light of the first wavelength and the laser light of the second wavelength are such that at least the incident angle of the incident angle and the outgoing angle with respect to the nonlinear optical element is a Brewster angle corresponding to the wavelength, the nonlinear optical element The reflection loss in can be reduced.

  In particular, if the laser light generator is configured as a solid-state laser device, deep ultraviolet light that continuously emits light in a wavelength region of about 200 nm or less can be obtained stably and efficiently with high efficiency by a small device. be able to.

  In addition, according to the optical device of the present invention, since the laser generator of the present invention is provided, the energy efficiency is high and the operation stability is high, using deep ultraviolet light that continuously emits light in a wavelength region of about 200 nm or less as a light source. It can be a device.

It is a top view showing the structure of the laser beam generator which concerns on the 1st Embodiment of this invention. It is an example of the optical path of the laser beam in the nonlinear optical element of the laser beam generator shown in FIG. FIG. 3 is a calculated value showing the refraction angle dependency of light of the second wavelength with respect to the nonlinear optical element of the sum frequency output in the laser beam generator shown in FIG. 1. FIG. 3 is a calculated value showing the refraction angle dependence of light of a first wavelength with respect to a nonlinear optical element with a sum frequency output in the laser light generator shown in FIG. 1. It is a top view showing the structure of the laser beam generator which concerns on the 2nd Embodiment of this invention. It is a top view showing the structure of the laser beam generator which concerns on the 3rd Embodiment of this invention. It is a figure showing the structure of the ultraviolet microscope which concerns on the 4th Embodiment of this invention. It is a figure showing the structure of the disk mastering apparatus which concerns on the 5th Embodiment of this invention. It is a figure for demonstrating the resonator finesse of the conventional laser beam generator.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The order of explanation is as follows.
1. First embodiment (laser light generator)
1-1. Modified example (modified example of the first embodiment)
2. Second embodiment (another laser beam generator)
3. Third embodiment (another laser beam generator)
4). Fourth embodiment (ultraviolet microscope)
5. Fifth embodiment (disk mastering device)

<1. First Embodiment>
FIG. 1 shows a schematic configuration of a laser beam generator according to a first embodiment of the present invention. The laser light generator 1 according to the present embodiment includes a first laser light generator 10 and a second laser light generator 11, and two different laser light generators 10 and 11 output from each other. The wavelength converter 12 mainly converts the wavelength of the laser beam having the wavelength and outputs the laser beam having the third wavelength.

The first laser light generator 10 outputs continuous ultraviolet light having a wavelength (λ ₁ ) within a range of 250 nm or more and 275 nm or less, and is assumed to oscillate at a single frequency here. The first laser beam oscillator 10 can be constituted by various lasers. For example, SHG may be generated using a gas laser such as an argon ion laser that has been used from the past, or a laser obtained by wavelength conversion of a semiconductor-excited solid-state laser that has recently been put into practical use. The latter is a solid-state laser device that is excited by a semiconductor laser, a semiconductor laser array, a semiconductor laser stack, a semiconductor laser-pumped solid-state laser, or the like, and has a higher efficiency than a conventional method that is excited by an arc lamp. Can be simplified. Further, using a laser device using a laser crystal such as Nd: YAG, Nd: YVO4, Nd: YLF, and Yb: YAG containing rare earth ions such as Nd and Yb, the fourth harmonic of 250 nm to 275 nm. The light may be generated. The first laser beam generator 10 may be capable of multimode oscillation.

On the other hand, the second laser light generator 11 outputs continuous light having a wavelength (λ ₂ ) within a range of 650 nm to 785 nm, for example, and is configured by a semiconductor laser that oscillates at a single frequency. . At this time, the semiconductor laser light may be amplified by a semiconductor amplifier or a solid-state laser amplifier in order to increase the output. Note that the second laser light generator 11 is not necessarily a single-frequency laser, and a semiconductor-excited solid-state laser can be used as the laser light generator 11 in addition to the above configuration. For example, a titanium sapphire laser, an Alexandrite laser, a Cr: LiCAF laser, a Cr: LiSAF laser, or the like is used as the second laser light generator 11. A laser excited with can be used. Examples of such a laser include a semiconductor-pumped solid state laser-pumped titanium sapphire laser, an Alexandrite laser, a Cr: LiCAF laser, and a Cr: LiSAF laser. Thereby, the laser beam generator 1 can be configured as an all-solid-state laser.

The wavelength converter 12 includes a first resonator 13 that resonates light having a wavelength λ ₁ output from the first laser light generator 10, and a wavelength λ ₂ that is output from the second laser light generator 11. The second resonator 14 that resonates light and the light (λ ₁ , λ ₂ ) amplified by the two resonators 13 and 14 are internally wavelength-converted to obtain a third wavelength (λ ₃ ). A nonlinear optical element 15 for generating light is provided.

Here, for example, a mirror 20 and an optical element 21 are disposed between the first laser beam generator 10 and the first resonator 13. The mirror 20 is used as needed, and may be two or more. The optical element 21 is for mode-matching the light having the wavelength λ ₁ to the first resonator 13, and a plurality of optical elements 21 may be used. Specifically, a lens, a mirror, a beam shaping prism, and a combination thereof are used. Further, for example, an optical element 22, a mirror 23, and an optical element 24 are disposed between the second laser light generator 11 and the second resonator 14. These are for making the light of wavelength λ ₂ enter the _second resonator 14 in a mode-matched state.

The first resonator 13 is an external resonator provided to resonate light having a wavelength λ ₁ , and includes an incident mirror 30 and three other mirrors 31, 32, and 33. A non-linear optical element 15 is disposed between the first and second optical elements 33. Here, it is desirable that the reflectance of the incident mirror 30 is optimized for impedance matching. Such a first resonator 13 is in a state in which mode match and impedance match are compatible, and resonates when the optical path length of the circuit (resonator length) is a certain value, and this optical path length is only the wavelength λ _1. Each time it changes, it becomes a resonance state. However, it is difficult to configure the resonator sufficiently firmly, and the resonance state is not always maintained unless the temperature change is small. Accordingly, it is preferable to provide a servo mechanism for holding resonance by the FM sideband method, polarization method, etc., and to this, a resonator length adjusting means such as a PZT element, a VCM element, a crystal having an electro-optic effect is provided. It is desirable to use in combination.

However, since the first wavelength λ ₁ is deep ultraviolet light having a wavelength of 250 nm or more and 275 nm or less, a normally used modulator such as KTP or LiNbO ₃ has low transmittance and is not suitable. In addition, since the BBO crystal, which is an electro-optic element having a high transmittance at such a wavelength, has a small electro-optic constant, it needs to be driven at a high voltage as both a phase modulator and an optical path length adjuster. For this reason, the polarization method is mainly used as a method for maintaining the resonance of the first resonator 13.

The second resonator 14 is an external resonator provided to resonate light having a wavelength λ ₂ , and includes an incident mirror 40 and three other mirrors 41, 42, and 43. 41, the nonlinear optical element 15 is arranged. Here, the second resonator 14 also has the same configuration as that of the first resonator 13, and similarly, it is desirable to set the reflectance of the incident mirror 40 to a value that impedance matches. It is also preferable to use an FM sideband method, a polarization method, or the like, or use a resonator length adjusting means such as PZT, as in the case of the first resonator.

Furthermore, one non-linear optical element 15 is arranged so as to be included in each of the two resonators 41 and 42, and the resonating light of wavelength λ ₁ and light of wavelength λ ₂ pass through the inside thereof. It is supposed to be. This non-linear optical element 15 is for performing sum frequency mixing, takes in light of wavelength λ ₁ and light of wavelength λ ₂ that resonate, and mixes them to generate light of the third wavelength λ ₃ . . Therefore, the nonlinear optical element 15 outputs the light of the third wavelength λ ₃ , and the light of the wavelength λ _{1 and} the light of the wavelength λ ₂ are also emitted, reflected by the mirror 33 and the mirror 41, respectively, and then mirrored again. 41, 42. Such a nonlinear optical element 15 includes, for example, BBO (β-BaB ₂ O ₄ ), CLBO (CsLiB ₆ O ₁₀ ), SBBO (Sr ₂ Be ₂ B ₂ O ₇ ), KBBF (KBe ₂ BO ₃ F ₂ ). Of any one of these crystals.

FIG. 2 shows a state in which light having wavelengths λ ₁ , λ _2, and λ ₃ is incident on and emitted from the nonlinear optical element 15. As described above, in the present embodiment, the light of wavelength λ _{1 and} the light of wavelength λ ₂ are incident on the nonlinear optical element 15 from the incident surface 15a in a state of being spatially separated from each other, and the wavelengths λ ₁ , λ ₂ and The light of wavelength λ ₃ is emitted from the emission surface 15b in a state of being spatially separated from each other, and each has a different optical path. That is, in the nonlinear optical element 15, the light of the wavelength λ _{1 and} the light of the wavelength λ ₂ partially overlap each other because of the request to perform sum frequency mixing, but they do not share the optical axis. . The reason for this is that when light of different wavelengths is shared by one optical axis, all optical elements on the optical path must simultaneously satisfy the conditions for loss reduction for all wavelengths passing through. Is difficult to set, and avoids optical surface and internal defects and damage to the coating material of the optical element that are easily caused by ultraviolet light superimposed on the shared optical axis. For example, the loss factor derived on the optical path of one wavelength does not cause a loss to the light of another wavelength.

The spatial separation of the light of wavelength λ _{1 and} the light of wavelength λ ₂ outside the nonlinear optical element 15 is set such that at least one of the incident angle and the emission angle of these lights is 30 ° or more. This can be achieved by birefringence (polarization dependence of refractive index). Here, the incident angles of the light of wavelength λ _{1 and} the light of wavelength λ _{2 on} the incident surface 15a are the Brewster angle θ _B. The Brewster angle is an angle at which the reflection of the p component of the s component and p component of polarized light incident at this angle is 0, and the refractive index at the incident surface 15a is n.
θ _B = tan ⁻¹ (n)
It is represented by The refractive index n varies depending on the wavelength and polarization state. Here, the light of wavelength λ _{1 and} the light of wavelength λ ₂ are incident on the incident surface 15 a at an angle θ _B corresponding to each wavelength. As a result, the reflection loss in the nonlinear optical element 15 can be reduced by using both the light of wavelength λ _{1 and} the light of wavelength λ ₂ as p-polarized light.

It is not necessary for the incident angles of the light of wavelength λ _{1 and} the light of wavelength λ _{2 on} the incident surface 15a to completely coincide with the Brewster angle θ _B , for example, within the range of the angle θ _B ± 5 °. It is also possible to select an angle near the angle θ _B. In this case, the reflection loss of p-polarized light is not zero, but the reflection loss can be reduced. Similarly, the exit angle can be selected for the exit surface 15b.

  Next, the setting method and effect of the above incident angle or output angle will be described with specific examples.

Even if light is incident / exited at an angle θ _B or an angle near the angle θ _B as described above, if the transmitted light is set to have a coaxial optical path inside the crystal, the light of wavelength λ _{1 and} the light of wavelength λ ₂ Are not incident at or near the angle θ _B due to dispersion. Therefore, there is a slight reflection loss at the crystal end face. This reflection loss circulates inside the resonator and doubles to increase the resonator loss. For example, when light having a wavelength of 266 nm is incident on the BBO crystal at an incident angle that completely matches the angle θ _B and is set so as to have a coaxial optical path inside the crystal and the light of wavelength 707 nm that is also incident on the BBO crystal, the wavelength 707 nm. The reflection loss of the light is 0.185% per surface, and when this light is input to the standing wave resonator, the loss is 0.740% in the round trip. Conversely, when light having a wavelength of 707 nm is incident on a BBO crystal at an incident angle that perfectly matches the angle θ _B and is set to have a coaxial optical path inside the crystal with the light having a wavelength of 266 nm, the reflection loss of the light having a wavelength of 266 nm is When the light is input to the ring resonator, the loss becomes 0.96% in the round.

In order to avoid the occurrence of this type of reflection loss, it is necessary to set so that transmitted light is spatially separated from each other inside the crystal. Therefore, when the incident angle is selected from the range between the angles θ _B of the light of wavelength 266 nm and the light of wavelength 707 nm, both are incident at an angle other than the angle θ _B , and loss is distributed to each light. think of. Incidentally, theta _B is 60.4 ° for light having a wavelength of 266 nm, theta _B light with a wavelength of 707nm is 59.0 °, although theta _B of the two wavelengths are in different, because they have very close values, Thus, even if one incident angle is selected, it is a good approximation for each θ _B. In this case, for example, the reflection loss of light with a wavelength of 266 nm can be 0.3% per surface, and the reflection loss of light with a wavelength of 707 nm can be 0.1% per surface. descend. Incidentally, in the conventional sum frequency generator configured as described above, the multiplication factor of the resonator is about 5 times. However, the multiplication factor of the resonator in the device configured as above is improved to about 30 times or more. It becomes possible to make it. When this is converted into finesse, it corresponds to about 100 or more.

In order to further reduce the reflection loss, it is preferable that the two transmitted lights are set so as to be spatially separated from each other, and at the same time, light of two wavelengths is incident at an angle as close as possible to the corresponding angle θ _B. Only when light of two wavelengths is incident at an angle θ _{B as} in the present embodiment, the reflection loss of the p component is both 0 and the loss is minimized.

However, it is only the p component of the polarized light that is reduced by incidence at an angle θ _B , and is not effective for s-polarized light. Therefore, it is preferable that the nonlinear optical element 15 is of type 1 phase matching because both of the two incident lights can be easily converted to the p component. From the viewpoint of loss as described above, the nonlinear optical element 15 here can be regarded as one that functions as one type of filter in the two resonators 13 and 14 and actively suppresses the resonator loss. In other words, the power of the incident light is held or amplified and consequently contributes to the sum frequency output.

Further, the light of wavelength λ _{1 and} the light of wavelength λ ₂ are spatially separated in this way, and these are made incident at an angle θ _B , so that the first resonator 13 and the second resonator 14 At least one finesse can be 100 or more. In general, finesse in a resonator is
F = π (R ₁ R _m ) ^1/4 / {1- (R ₁ R _m ) ^1/2 } (1)
(R ₁ ; incident mirror reflectivity, R _m ; product of effective light utilization in other mirrors and optical elements in the resonator)
Given by. The effective light utilization rate is a reflectance for a mirror and a transmittance for an optical element. If R ₁ can be selected so that impedance matching can be taken,
R ₁ = R _m ≡R
And in R-1
F to π / (1-R) (2)
It becomes. For example, in the first resonator, it is assumed that the incident mirror 30 is selected so as to be approximately R ₁ = R _m and incident at an angle θ _B so that the loss in the nonlinear optical element 15 can be ignored. At this time, according to the formula (2), the reflectance R _m of the other mirrors 31 to 33 can be about 97% or more and the F value can be 100 or more. It is actually possible to set the reflectances R ₁ and R _m to 97% or more, and even if absorption / scattering in the nonlinear optical element 15 is taken into account, it is sufficiently possible to make the F value 100 or more. is there. Further, the reflectance R ₁ , R _{m is set} to 99% or more, and the non-linear optical element 15 is absorbed and scattered by using a high-quality BBO crystal manufactured by, for example, pulling up the direct method (C2 method). If the reflectance of the incident mirror 30 is increased, for example, by setting it to 0.5% or less, the F value can be increased to as high as 300 or more. The same applies to the second resonator.

It should be noted that such a laser beam generator having a resonator finesse of 100 or more actually has structural requirements in the present embodiment (that is, the light of wavelength λ _{1 and} the light of wavelength λ ₂ are converted into nonlinear optical elements. 15 is incident only at an angle θ _B or an angle near the angle θ _B. For example, in the conventional laser beam generator described in Japanese Patent Laid-Open No. 10-341054, the optical path from the mirror 1223 to the mirror 1224 is shared by the first resonator and the second resonator as shown in FIG. The two laser beams on this optical path are not incident on the BBO crystal 1226 at the angle θ _B as described above. Therefore, a reflection loss always occurs at the crystal end face of the BBO crystal 1226. Even if the BBO crystal 1226 is provided with a reduced reflection coating, the transmittance is considered to be about 95% due to residual reflection, which is considered a technical limit.

In addition, in this case, it is necessary to manipulate the two conditions of reflectance and transmittance so that the light having the wavelength λ ₁ is reflected and the light having the wavelength λ ₂ is transmitted to the mirrors 1223 and 1224. When the separation mirrors 1223 and 1224 are actually manufactured, if the light with the wavelength λ ₂ is set to transmit, for example, 98% or more, the upper limit of the reflectance with respect to the light with the wavelength λ ₁ is estimated to be about 99%. Therefore, in the first resonator, even if the reflectance of the remaining mirror 1222 is as high as 99.5%, for example, R _m = (0.99) ² × 0.995 × 0.95 , R _m is considered to have an upper limit of about 92.6%. Therefore, when R ₁ is selected so that R ₁ = R _m = 0.926, the finesse of the first resonator is estimated to be 13.2 from Equation (2).

To further increase the R _m of the first resonator (1) both end faces of the BBO crystal 1226 is cut at an angle theta _B, the incident angle of the laser beam and the angle theta _B, (2) separation mirror 1223 , 1224 to increase the reflectance of the first wavelength light, and (3) to increase the reflectance R ₁ of the incident mirror 1221. However, in (2), on the contrary, the transmittance for the light of the second wavelength is lowered, and in (3), the finesse of the second resonator is greatly impaired, and the overall efficiency is reduced. Incidentally, increasing the overall efficiency until the last minute of 99% and R ₁ at the expense, finesse F of the first resonator is 73.8% resonator with laser light generating apparatus having such a structure finesse It can be seen that it is substantially difficult to set the value to 100 or more.

In the above-described conventional apparatus by Watanabe et al., A prism is used in place of the separation mirror, and although finesse is improved, the reflectance R ₁ of the incident mirror is 10%. R _m is estimated to be approximately 82% and finesse is estimated to be approximately 20. The reason why the finesse is low in this way depends on the quality of the prisms and BBO crystals (made by the flux method) used, but the biggest factor is the two wavelengths of the anti-reflection coating material attached to the BBO crystals. This is considered the performance limit for designing.

On the other hand, the apparatus by Berkeland et al. Uses Brewster cut BBO crystal to prevent resonator loss due to the anti-reflection coating (DJ Berkeland, et.al., Applied Optics, vol.36, No.18, pp4159). -4162 (1997)). However, in this case, considering internal absorption due to the quality of the BBO crystal (prepared by the flux method), R ₁ = 91%, and as a result, the finesse remains at about 51 (R _m -97.6%). ing. From this, it can be seen that the use of a high-quality crystal with little absorption or scattering as the nonlinear optical element 15 is also a condition for improving finesse.

(1-1. Modification)
If the light of wavelength λ _{1 and} the light of wavelength λ ₂ are set so as to be spatially separated from each other in the nonlinear optical element 15 as in the first embodiment, the overlapping of these beams is small. There is a possibility that the sum frequency conversion efficiency is lowered. However, if the resonator loss typified by the reflection loss described above can be effectively reduced, the sum frequency output can be increased while compensating for the reduction in conversion efficiency. Here, another method for setting the incident angle or the outgoing angle will be described from such a viewpoint.

As described above, it is necessary to set the transmitted light so as to be spatially separated from each other in order to reduce loss. This state is actually obtained by widening the difference in the incident angle (hereinafter referred to as the separation angle) between the light of wavelength λ _{1 and} the light of wavelength λ ₂ on the incident surface 15a and providing a difference in the respective refraction angles. Realized. Therefore, consider actively increasing the separation angle here.

That is, the separation angle is increased outside the nonlinear optical element 15 while maintaining the state in which the two incident lights of the light having the wavelength λ _{1 and} the light having the wavelength λ ₂ can sufficiently contribute to the generation of the sum frequency inside the nonlinear optical element 15. Thus, the optical path of the incident light is adjusted. Here, in order to spatially separate the two incident lights, it is necessary that the separation angle Δθ be larger than the beam divergence angle φ (relative intensity 1 / e ² full width) of the incident light (Δθ> φ). Furthermore, in order to sufficiently separate the light having the wavelength λ ₃ output from the nonlinear optical element 15, it is important that Δθ> 2φ. However, it should be noted that if the separation angle Δθ is increased excessively, the spatial overlap of the incident light beams decreases.
Lδθ << D
(L: length of nonlinear optical element 15, δθ; increment of separation angle inside nonlinear optical element 15, D: average beam diameter of incident light inside nonlinear optical element 15)
In this case, the sum frequency output is not greatly affected. At this time, if the separation angle is set to a non-critical direction of the phase matching angle (a direction in which the angle of the crystal axis of the nonlinear optical element 15 with the c axis is constant), a decrease in output due to phase mismatching is suppressed. be able to.

An example of a modification is shown below. Here, the wavelength λ ₁ is 707 nm, the wavelength λ ₂ is 206 nm, the wavelength λ ₃ of the generated sum is 193.3 nm, and a BBO crystal that is phase-matched as type 1 as the nonlinear optical element 15 is used here. Used. Both the incident light of wavelength λ ₁ and wavelength λ ₂ are parallel light having a diameter of 250 μm, and are continuous waves with a constant output. Further, at both the wavelength λ ₁ (707 nm) and the wavelength λ ₂ (206 nm), the incident mirror reflectivity R ₁ = 0.99, and the resonator reflectivity R _m = 0.99 excluding the incident mirror and the BBO crystal is incident. It is assumed that the phase matching condition is always satisfied in the direction perpendicular to the surface 15a. Further, from Kato's Sellmeier equation (Kato, Laser Research, vol. 18, p3 (1990)), the refractive indices of the nonlinear optical element 15 of wavelengths λ ₁ , λ ₂ , and λ ₃ with respect to the incident surface 15a are 1.6638, respectively. , 1.7585, 1.7326. For the sake of simplicity, the sum frequency output is assumed to be proportional to the beam intensity of the incident light having the wavelengths λ ₁ and λ ₂ inside the nonlinear optical element 15 and the integral of the spatial overlap of the beams. Here, however, the spatial overlap of the beams does not mean that they share the optical axis.

(I) With respect to light of wavelength λ ₁ (707 nm), the incident angle is fixed at 59 °, which is the angle θ _B , and the refraction angle is fixed at 31 °. Next, in this state, the incident angle of the light of wavelength λ ₂ (206 nm) is changed and fixed at the position where the sum frequency output becomes maximum. FIG. 3 shows the relationship between the refraction angle of light of wavelength λ ₂ (206 nm) and the relative sum frequency output in this case. From the figure, the relative sum frequency output becomes maximum when the refraction angle of the light of wavelength λ ₂ is 30.4 °. Thus, it can be seen that there is a maximum value in the sum frequency output, and that the separation angle Δθ is not simply large but an optimum value exists. Therefore, in this way, the optical path of the two incident lights can be spatially separated and defined under simple and optimum conditions. At the same time, the light of wavelength λ _{1 and} the light of wavelength λ ₂ are coaxial at a refraction angle of 31 °, but it can be seen that the output is maximized not when the optical path is shared.

(Ii) For light with a wavelength λ ₂ (206 nm), the incident angle is fixed at 60.4 °, which is the angle θ _B , and the refraction angle is fixed at 29.6 °. In this state, the incident angle of the light of wavelength λ ₁ (707 nm) is changed and fixed at the position where the sum frequency output becomes maximum. FIG. 4 shows the relationship between the refraction angle of light of wavelength λ ₁ (707 nm) and the relative sum frequency output in this case. From the figure, it can be seen that the relative sum frequency output is maximized when the refraction angle of the light of wavelength λ ₁ is 29.9 ° and is optimized at this position. The light of wavelength λ _{1 and} the light of wavelength λ ₂ are coaxial at a refraction angle of 29.6 °, but in this case as well, the output is maximized not when the optical path is shared.

In these examples, the incident angle on the fixed side is θ _B , but the incident angle may be selected within a range of approximately θ _B ± 5 °.

According to this method, there is a possibility that the resonator loss increases due to the deviation of the incident angle from the angle θ _B or the sum frequency conversion efficiency decreases because the beam overlap of the two incident lights decreases. Since it is not necessary to provide a wavelength separation mirror in the resonator due to spatial separation of incident light, it is possible to greatly reduce the intracavity loss, and as illustrated, overall efficiency can be increased.

Further, depending on the combination of wavelength and polarization, the type of nonlinear optical element 15, and the like, for example, when the dispersion and birefringence of the light with wavelength λ _{1 and} the light with wavelength λ ₂ are small, or when the divergence angle of the beam is large Arise. In such a case, if the method of the present modification is used, it is possible to guide the light so as to increase the separation angle, and reliably separate the light having the wavelength λ _{1 and} the light having the wavelength λ ₂ as incident light.

Further, by manipulating the separation angle in this way, for example, when the separation angle is greatly expanded so that the incident angle of the light of wavelength λ ₁ and the wavelength λ ₂ is larger than the angle θ _B , the nonlinear optical element 15 and the mirror 33 and The distance to the mirror 41 is shortened, and the laser beam generator 1 can be reduced in size. By the way, the above-mentioned device by Berkeland et al. Does not have a sufficiently large separation angle, so designing it to minimize loss or maximum conversion efficiency increases the distance from the nonlinear optical element to the reflecting mirror, which increases the size of the device. It will be. This apparatus is excellent as a light source for spectroscopic use in a laboratory, for example, but is not suitable for industrial use.

  Hereinafter, the first embodiment will be described together with modifications.

In this way, in the laser beam generator 1 that has determined the optical paths of the light of wavelength λ _{1 and} the light of wavelength λ ₂ , the optical path adjustment is performed to translate the nonlinear optical element 15 so as to move in the same plane as the incident surface 15a. If a mechanism is provided to move and adjust the optical paths of the light of wavelength λ _{1 and} the light of wavelength λ ₂ , fine adjustment of the relative position of the optical path can be easily performed. Thus, it is preferable to adjust the beam overlap position and the overlap amount of the light of wavelength λ _{1 and} the light of wavelength λ _{2 because} the output can be adjusted or optimized. At this time, if the nonlinear optical element 15 is configured so that the incident surface 15a and the emitting surface 15b are vertical and all the optical paths of the laser light in the laser light generating device 1 are in one horizontal plane, the optical path adjustment becomes easy.

Further, the deep ultraviolet light having the wavelength λ ₃ that is finally obtained is emitted from between the light having the wavelength λ _{1 and} the light having the wavelength λ ₂ as shown in FIG. Accordingly, the light of wavelength λ ₃ is not used by using a wavelength separation element such as a prism, but only an element having a spatial separation function such as an aperture is used in combination, and the size and position of the mirror 33 and the mirror 41 are devised. It is also possible to take it out. Considering that the transmittance of the wavelength separation film for the wavelength λ ₃ is not so large at present, this is an effective output method.

  Such a laser beam generator 1 operates as follows, for example.

First, light having a wavelength λ ₁ is output from the first laser generator 10. The light having the wavelength λ ₁ is input to the first resonator 13 of the wavelength conversion unit 12 via the mirror 20 and the optical element 21. In the first resonator 13, the light of wavelength λ ₁ circulates around the mirrors 30, 31, 32, the nonlinear optical element 15, and the mirror 33 in this order and is resonated. In addition, light of wavelength λ ₂ is output from the second laser generator 11. The light having the wavelength λ ₂ is input to the second resonator 14 of the wavelength conversion unit 12 through the optical element 22, the mirror 23, and the optical element 24. In the second resonator 14, the light of wavelength λ ₂ circulates around the mirror 40, the nonlinear optical elements 15, 41, 42, and the mirror 43 in this order and is resonated. At this time, the non-linear optical element 15 generates a sum frequency of the wavelength λ ₃ by the light of the wavelength λ _{1 and} the light of the wavelength λ ₂ , and just passes between the mirror 33 and the mirror 41 and is output from the wavelength converter 12. The

  While the wavelength width of the sum frequency output is variously set according to demands for speckle reduction, lens chromatic aberration, and interferometer coherence length, for example, the line width or bandwidth of the first laser generator and the second laser generator Can be classified step by step. That is, when a simple band limitation is applied to a solid-state laser, the wavelength width of output light is 10 pm or less, and when a solid or semiconductor laser is sandwiched to an extent corresponding to the bandwidth of a gas laser, 1 pm or less. In the case where the laser beam has a single frequency, it can be 0.1 pm or less.

As described above, in the laser light generation device 1 of the present embodiment, the light with the wavelength λ _{1 and} the light with the wavelength λ ₂ are incident on the nonlinear optical element 15 from the incident surface 15a in a state of being spatially separated from each other. Since light of λ ₁ , wavelength λ _2, and wavelength λ ₃ is emitted from the emission surface 15b in a state of being spatially separated from each other, and has different optical paths, the first resonator 13 and the second resonance As a result of the loss reduction, high resonator finesse is obtained as a result of the loss reduction, and the conversion efficiency in the sum frequency mixing is improved. In particular, since the output light is already spatially separated on the emission surface 15b, it is not necessary to provide a wavelength separation mirror in the wavelength conversion unit 12, and loss can be greatly reduced.

  In addition, since the first resonator 13 and the second resonator 14 do not share the optical path in the inside thereof, even if one of them is damaged, no loss occurs in the other, and by any chance the resonator 13 or the resonator 14 Even if a loss occurs, an increase in the resonator loss as a whole is prevented, and the device can be operated more stably for a long time. In addition, the coating which satisfies the loss reduction conditions for all transmitted light as applied to the element 15 in the conventional resonator is unnecessary, the optical loss due to such coating can be omitted, and the apparatus is configured simply. In addition, the cost can be reduced.

Further, since the incident angles of the light of wavelength λ _{1 and} the light of wavelength λ _{2 on} the incident surface 15a are set to the Brewster angles θ _B corresponding to the respective wavelengths, the reflection loss in the nonlinear optical element 15 can be reduced.

  Furthermore, since the first laser light oscillator 10 and the second laser light oscillator 11 generate continuous ultraviolet light, such a laser light generator 1 is more advantageous for speckle removal than pulse light. For example, it can be applied as an inspection apparatus such as a microscope or a semiconductor because it can be a simple illumination light and is less likely to damage the subject.

  Since the laser light generator 1 including the first laser light generator 10 and the second laser light generator 11 is configured as an all-solid-state laser device, for example, external cooling required in the case of a gas laser device Water piping and a large-capacity power supply are not required, and the scale of the apparatus can be reduced. Moreover, if it is an all-solid-state laser apparatus, it will become easy to acquire a favorable wavelength characteristic stably, even if it enlarges output. Since the second laser light generator 11 is constituted by a semiconductor laser that oscillates at a single frequency, the absolute wavelength can be easily stabilized with a certain accuracy.

<2. Second Embodiment>
FIG. 5 shows a schematic configuration of a laser beam generator according to the second embodiment of the present invention. This laser beam generator 2 is the same as the laser beam generator 1 according to the first embodiment, except that the second laser beam generator 16 is provided inside the second resonator 14. A means (not shown) for exciting the second laser light generator 16 by an output such as current or current is connected. Therefore, in the first embodiment, the second resonator 14 is an external resonator of the second laser light generator 11, but here, the second laser light is placed inside the second resonator 14. The laser medium called the generator 16 is configured to be incorporated, and both are integrated. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The second laser light generator 16 is provided between the mirror 42 and the mirror 43 in the second resonator 14, and has a wavelength in the range of, for example, 650 nm to 785 nm, similarly to the second laser light generator 11. (Λ ₂ ) continuous ultraviolet light is output. The constituent material is the same as that of the second laser light generator 11, and for example, a semiconductor laser or a solid-state laser such as titanium sapphire, alexandrite, Cr: LiCAF, CrLiSAF, or the like can be used. The second laser light oscillator 16 outputs light and amplifies the output light through the second resonator 14 at the same time.

Such a laser beam generator 2 outputs a sum frequency in the same manner as the laser beam generator 1. At this time, in the second resonator 14, light having a wavelength λ ₂ circulates in an optical path constituted by the mirrors 40 to 43 and the second laser light generator 16, and a gain larger than that in the case of simply resonating is obtained.

Therefore, according to the present embodiment, the light of wavelength λ ₂ is amplified by the second laser light generator 16 itself and is incident on the nonlinear optical element 15 with a large light output. Can be improved. In the present embodiment, the same effect as in the first embodiment can be obtained.

<3. Third Embodiment>
FIG. 6 shows a schematic configuration of a laser beam generator according to the third embodiment of the present invention. This laser light generating device 3 is obtained by adding a laser gain medium 44 as an amplifier inside the second resonator 14 in the laser light generating device 1 in the first embodiment. This is one amplification scheme called injection locking. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The laser gain medium 44 is provided between the mirror 42 and the mirror 43 in the second resonator 14 so as to actively increase the gain of the resonator 14 in response to an input from a master laser (not shown). It has become. As the master laser, a low-power semiconductor laser or solid-state laser may be used. As the laser gain medium 44, for example, a semiconductor amplifier or a solid such as titanium sapphire crystal, alexandrite crystal, Cr: LiCAF crystal, Cr: LiSAF crystal, etc. A gain medium or the like can be used. Of these, when a solid gain medium is used, the laser gain medium 44 is preferably pumped by a semiconductor laser or a semiconductor laser pumped solid laser in terms of size reduction and high efficiency.

Such a laser beam generator 3 outputs a sum frequency in the same manner as the laser beam generator 1. At this time, in the second resonator 14, light having a wavelength λ ₂ circulates in an optical path constituted by the mirrors 40 to 43 and the laser gain medium 44, and a gain larger than that in the case of simply resonating is obtained.

Therefore, according to the present embodiment, the light having the wavelength λ ₂ is incident on the nonlinear optical element 15 with a large light output amplified by the laser gain medium 44, so that the sum frequency output can be improved. In the present embodiment, the same effect as in the first embodiment can be obtained.

<4. Fourth Embodiment>
FIG. 7 shows a schematic configuration of an ultraviolet microscope according to the fourth embodiment of the present invention. The ultraviolet microscope 100 includes a laser beam generator 101, an optical system 102, a beam splitter 103, an objective lens 104, a stage 106 for placing a test object 105, an imaging optical system 107, an image acquisition unit 108, an image conversion unit. A unit 109 and an image display unit 110 are provided. Here, the laser beam generator 101 is the laser beam generator of the present invention, and is configured by any one of the first to third embodiments, for example. The optical system 102 has functions such as beam shaping, speckle reduction, uniform beam formation, beam deflection, polarization control, light amount adjustment, and diaphragm, and includes optical elements such as lenses, mirrors, and prisms. It is configured. Further, the beam splitter 103 may be a polarizing beam splitter. In that case, a quarter wavelength plate may be inserted between the beam splitter 103 and the objective lens 104. Examples of the test object 105 include a semiconductor substrate, a semiconductor integrated circuit, an optical element, a liquid crystal substrate, a liquid crystal functional element, a disk head, a living body, and other objects having a fine structure that reflects and scatters part of ultraviolet rays. Can be mentioned.

  The image acquisition unit 108 acquires information on an image obtained in the imaging optical system 107 as an optical signal, converts the acquired image information into an analog signal, and outputs it. For example, a CCD (Charge Coupled) is connected to a photodiode array. Device (Charge Coupled Device) is connected to a CCD imaging device, an imaging tube, or the like. The image conversion unit 109 converts and outputs an analog signal input from the image acquisition unit 108 into a digital signal, and includes an A / D converter or the like. Further, the image display unit 110 reproduces and displays an image from the digital signal input from the image conversion unit 109, and can be configured by various display devices. Although not shown, the ultraviolet ray inspection apparatus 100 is provided with a specimen transport device, a shield, an autofocus device, a vibration isolator, and the like.

  Such an ultraviolet ray inspection apparatus 100 operates as follows. That is, ultraviolet light is output from the laser light generation device 101, and the optical system 102 performs space uniformization, shaping, time uniformization, and light amount adjustment on the light. Subsequently, when light enters the beam splitter 103, a part of the light enters the objective lens 104 and is irradiated to the test object 105 placed on the stage 106.

  Next, the light transmitted from the test object 105 through the objective lens 104 and reaching the beam splitter 103 is further projected onto the image acquisition device 108 via the imaging optical system 107. Here, the distance between the objective lens 104 and the test object 105 is changed by an autofocus mechanism (not shown), and the image obtained by the image acquisition unit 108 is adjusted to be a conjugate image obtained by enlarging the test object 105. Autofocus methods use changes in image resolution, irradiate light from another light source to adjust the focal position of this beam, and detect changes in the capacitance of the space created by the sensor and the test object Various types can be used, such as what to do.

  Further, in the image acquisition unit 108, the light projected from the imaging optical system 107 is acquired as a signal, converted into an analog signal, and output to the image conversion unit 109. The image conversion unit 109 performs A / D conversion of the signal, enlarges / reduces the image, adds a user function, converts the format for saving the data, and the like. 110. Finally, the image display unit 110 reproduces and displays an image from the digital signal input from the image conversion unit 109.

  According to such an ultraviolet microscope 100, a continuous wave of about 200 nm or less is output to the laser light generator 101 of the present invention by using the laser light generator of the present invention. Compared to this, it is possible to acquire and analyze a higher resolution image. In addition, since the output of the ultraviolet microscope 100 is a continuous wave, it is possible to suppress damage to the optical system and the test object as compared with the pulse light source having the same wavelength as the speckle reduction. Therefore, for example, non-destructive inspection can be performed even in a field where conventional non-destructive inspection cannot be performed by a high-resolution measurement method typified by semiconductor wafers, semiconductor patterns, liquid crystal patterns, reticles, fluorescent substances such as living bodies, etc. Can be expanded, and the object of the test object can be expanded. Furthermore, since the laser light generation device of the present invention is used for the laser light generation device 101, a vacuum is not required, so that the throughput can be increased.

  Note that the image conversion unit 109 and the image display unit 110 can be configured to include a computer such as a personal computer, for example, and the image conversion unit 109 or the image display unit 110 has an application program for image analysis, image data analysis, and the like. Can be installed. In addition, a data input / output device, a user interface, a special filter, or the like can be attached to the ultraviolet microscope 100 as necessary. In this way, various functions including image processing can be added.

  Accordingly, various inspection apparatuses such as a semiconductor inspection apparatus, a mask inspection apparatus, a liquid crystal inspection apparatus, and a disk head inspection apparatus can be configured as well as an ultraviolet microscope. For example, by adding a wafer transport mechanism, a data input / output unit, a data storage unit, a defect classification program, statistical software, and the like to the ultraviolet microscope 100, a semiconductor inspection apparatus for inspecting a semiconductor wafer or a semiconductor integrated circuit is obtained. Can do. Further, a mask inspection apparatus can be formed by using the test object 105 as a mask or a reticle, and can also be configured as a disk head inspection apparatus capable of inspecting a fine structure such as a hard disk substrate or a head gap. Furthermore, if the absorption characteristic of ultraviolet rays is used, a structure that transmits visible light and cannot be seen normally can be observed. For example, defects and structures such as liquid crystal can be determined. In any of the inspection apparatuses, it is possible to inspect with high resolution by reducing noise due to damage to the test object or speckles.

  In addition, even a substance that absorbs less light in the wavelength range conventionally used in microscopes often absorbs wavelengths of 200 nm or less. Therefore, when the energy stored in the substance by such absorption is re-emitted as fluorescence generated from defects, impurities, intentionally added markers, etc., if this fluorescence is detected, an ultraviolet microscope 100 can be used as a fluorescence microscope for inspecting the purity of a substance, the type, concentration, and active state of impurities.

<5. Fifth embodiment>
FIG. 8 shows a schematic configuration of a disk mastering apparatus 200 according to the fifth embodiment of the present invention. The disk mastering apparatus 200 includes a laser light generator 201, an optical system 202, a mirror 203, an objective lens 204, a master disk 205, and a stage 206. Here, the laser beam generator 201 is the laser beam generator of the present invention, and is configured by any one of the first to third embodiments, for example. The optical system 202 has functions such as beam shaping, a light amount adjustment device, a multi-beam generation device, a modulator, a beam deflector, polarization control, and an aperture, and includes optical elements such as lenses, mirrors, and prisms. It consists of Furthermore, the mirror 203 is for adjusting the traveling direction of the laser beam from the laser beam generator 201 in the direction of the stage 206, and may be a beam splitter. The stage 207 is for mounting the master disk 205 and has a function of rotating and translating. The disk mastering device 200 is provided with a data reproducing device, a format encoder, a stage control device, a vibration isolator and the like (not shown).

In this disk mastering apparatus 200, the laser light output from the laser light generating apparatus 201 is irradiated onto the master disk 205 on the stage 206 via the optical system 202, the mirror 203, and the objective lens 204, and the master disk A spot is formed at a desired position on the surface of 205. At this time, the diameter d of the spot formed on the surface of the master disk 205 is approximately
d = 1.22λ / NA
(Λ is the wavelength of the laser beam, NA is the numerical aperture)
Therefore, when lenses having the same numerical aperture are used, a spot that is about 30% smaller than a 266 nm laser, which is a wavelength of a conventionally available continuous wave laser, is formed. According to this, it is theoretically possible to expect an improvement in recording density of about twice.

  Thus, according to the disk mastering apparatus 200, the laser light generating apparatus 201 of the present invention is used as the light source laser light generating apparatus 201 and a continuous wave with a wavelength of about 200 nm or less is output. Thus, it is possible to form a spot that is 20% or smaller. Therefore, a master disk having a high recording density can be produced.

The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the first embodiment, the first resonator 13 is configured by the mirrors 30 to 33 as shown in FIG. 1, but the structure of the resonator 13 is not limited to this, and may be appropriately selected. It can be changed. That is, the number of mirrors need not be limited to four. For example, an element other than a mirror such as a prism may be used. By using such an optical element, the number of mirrors may be one to three. It is good also as four or more sheets. Here, the light of wavelength λ ₁ is made incident on the first resonator 13 from the mirror 30, but it is also possible to make the light enter from the mirror 32 side using the mirror 32 as the incident mirror. Similarly, the configuration of the second resonator 14 can be changed as appropriate, and the mirror 40 may not be the incident mirror, but another mirror, for example, the mirror 42 may be the incident mirror. Note that the configuration of the resonator is the same as that of the first embodiment in the second and third embodiments, and the same change can be made.

  1, 2, 3, 101, 201... Laser light generator, 10... First laser generator, 11, 16... Second laser generator, 12... Wavelength converter, 13. DESCRIPTION OF SYMBOLS 2nd resonator, 15 ... Nonlinear optical element, 20, 23, 30-33, 40-43 ... Mirror, 21, 22, 24 ... Optical element, 44 ... Laser gain medium, 102, 202 ... Optical system, 103 DESCRIPTION OF SYMBOLS ... Beam splitter, 104, 204 ... Objective lens, 105 ... Test object, 106, 206 ... Stage, 107 ... Imaging optical system, 108 ... Image acquisition apparatus, 109 ... Image conversion part, 110 ... Image display part, 203 ... Mirror, 205 ... Master disk

Claims (19)

A first laser generator that outputs laser light of a first wavelength, and a first resonator that resonates the laser light of the first wavelength;
A second laser generator that outputs laser light of a second wavelength, and a second resonator that resonates the laser light of the second wavelength;
It is arranged so as to be included in the first resonator and the second resonator, and is emitted from an incident surface on which laser light of the first wavelength and laser light of the second wavelength are incident on both ends. A nonlinear optical element each having an exit surface,
In the laser beam generator for generating the laser beam of the third wavelength by the sum frequency mixing of the laser beam of the first wavelength and the laser beam of the second wavelength that passes through the inside of the nonlinear optical element,
The incident angles of the laser light of the first wavelength and the laser light of the second wavelength with respect to the nonlinear optical element are Brewster angles corresponding to wavelengths, and the nonlinear optical element has a type 1 phase matching. To do,
The laser light of the first wavelength and the laser light of the second wavelength are incident on the nonlinear optical element from the incident surface in a state where beam central axes are spatially separated from each other,
The laser light of the first wavelength, the laser light of the second wavelength, and the laser light of the third wavelength are emitted from the emission surface with the beam center axes spatially separated from each other, and are different from each other. Has an optical path, and
Inside the nonlinear optical element, the laser light of the first wavelength and the laser light of the second wavelength partially overlap, but the optical axis is not shared,
The difference in the incident angle (separation angle Δθ) of the laser light of the first wavelength and the laser light of the second wavelength with respect to the nonlinear optical element is the laser light of the first wavelength and the first wavelength of the nonlinear optical element. Greater than twice the beam divergence angle (φ) of the incident light of the laser light having the wavelength of 2,
Laser light generator. Optical path adjustment means for moving and adjusting the optical paths of the laser light of the first wavelength and the laser light of the second wavelength by translating the nonlinear optical element so as to move in the same plane as the incident surface. The laser beam generator according to claim 1. The nonlinear optical element is any one of BBO (β-BaB ₂ O ₄ ), CLBO (CsLiB ₆ O ₁₀ ), SBBO (Sr ₂ Be ₂ B ₂ O ₇ ), and KBBF (KBe ₂ BO ₃ F ₂ ). The laser beam generator according to claim 1, comprising: The laser beam generator according to claim 3, wherein the nonlinear optical element is a BBO (β-BaB ₂ O ₄ ) crystal manufactured by a direct pulling method. The laser light generator according to claim 1, wherein a resonator finesse of at least one of the first resonator and the second resonator is 100 or more. The laser light generator according to claim 1, wherein the first resonator is an external resonator, and the second resonator is a laser amplifier or an external resonator. The laser light generator according to claim 1, wherein the second laser generator is a semiconductor laser or a semiconductor laser excitation solid-state laser. The laser beam generator according to claim 1, wherein the second laser generator oscillates or resonates at a single frequency. The laser beam generator according to claim 7, wherein the second laser generator is any one of a titanium sapphire laser, an alexandrite laser, a Cr: LiCAF laser, and a Cr: LiSAF laser. The laser beam generator according to claim 1, wherein the second resonator is a semiconductor amplifier or a solid-state laser amplifier. The laser beam generator according to claim 10, wherein the second resonator amplifies the laser beam of the second wavelength by injection locking using the semiconductor laser as a master laser. The laser beam generator according to claim 10, wherein the solid-state laser amplifier is composed of any one of a titanium sapphire crystal, an alexandrite crystal, a Cr: LiCAF crystal, and a Cr: LiSAF crystal. The laser beam generator according to claim 10, wherein the solid-state laser amplifier is excited by a semiconductor laser or a semiconductor laser-pumped solid-state laser. 2. The laser beam generator according to claim 1, wherein at least one of the first resonator and the second resonator includes an optical path length adjusting unit that makes an optical path length variable. 3. The laser beam generator according to claim 14, wherein the optical path length adjusting unit includes any one of a PZT element, a VCM element, and an electro-optic crystal. The laser beam generator according to claim 14, wherein at least one of the first resonator and the second resonator maintains a resonance state by an FM sideband method or a polarization method using the optical path length adjusting means. The first wavelength is in a range from 250 nm to 275 nm, the second wavelength is in a range from 650 nm to 785 nm, and the third wavelength is in a range from 180 nm to 204 nm. Item 2. A laser beam generator according to Item 1. The laser beam generator according to claim 1, wherein the wavelength width of the third wavelength laser beam is 10 pm or less. A first laser generator that outputs laser light of a first wavelength, a first resonator that resonates the laser light of the first wavelength, and a second laser generator that outputs laser light of a second wavelength And a second resonator that resonates the laser light of the second wavelength, and the first resonator and the second resonator are disposed so as to be included in the first resonator, and the first wavelength is provided at both ends. A laser generating means including a nonlinear optical element each having an incident surface on which the laser beam of the second wavelength and a laser beam of the second wavelength are incident and an emitting surface that emits the laser beam,
A laser beam having a third wavelength obtained by sum frequency mixing of the laser beam having the first wavelength and the laser beam having the second wavelength that passes through the inside of the nonlinear optical element is generated from the laser generating unit. In an optical device,
The incident angles of the laser light of the first wavelength and the laser light of the second wavelength with respect to the nonlinear optical element are Brewster angles corresponding to the wavelengths, and the nonlinear optical element performs type 1 phase matching. And
The laser light of the first wavelength and the laser light of the second wavelength are incident on the nonlinear optical element from the incident surface in a state where beam central axes are spatially separated from each other,
The laser light of the first wavelength, the laser light of the second wavelength, and the laser light of the third wavelength are emitted from the emission surface with the beam center axes spatially separated from each other, and are different from each other. Has an optical path, and
Inside the nonlinear optical element, the laser light of the first wavelength and the laser light of the second wavelength partially overlap, but the optical axis is not shared,
The difference in the incident angle (separation angle Δθ) of the laser light of the first wavelength and the laser light of the second wavelength with respect to the nonlinear optical element is the laser light of the first wavelength and the first wavelength of the nonlinear optical element. Greater than twice the beam divergence angle (φ) of the incident light of the laser light having the wavelength of 2,
Optical device.

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